Process of making a carbon fiber nonwoven fabric

ABSTRACT

The present invention has an object of providing the carbon fiber (or the nonwoven fabric configured of the aforementioned carbon fiber) of which the surface area, the graphitization degree, and the fiber diameter are large, high, and small, respectively, and yet of which dispersion is small. 
     The method of producing the carbon fiber nonwoven fabric includes a dispersion liquid preparing step of preparing a dispersion liquid containing resin and pitch, an electrospinning step of producing the nonwoven fabric that is comprised of carbon fiber precursors with electrospinning from the aforementioned dispersion liquid, and a modifying step of modifying the carbon fiber precursors of the nonwoven fabric obtained in the aforementioned electrospinning step into the carbon fiber.

TECHNICAL FIELD

The present invention relates to carbon fiber.

BACKGROUND ART

An attention is paid to the carbon fiber in a field of batteries (forexample, a lithium-ion battery and an electric double-layer capacitor)and fuel cells. In particular, an attention is paid to the carbon fibernonwoven fabric as an electrode material of the aforementionedbatteries. The aforementioned nonwoven fabric is configured of thecarbon fiber of which a fiber diameter is 10 μm or so.

Recently, the nonwoven fabric configured of the carbon fiber of whichthe fiber diameter is 10 μm or less (for example, 1 μm 0 or so) has beenrequired from a viewpoint of an augment in a surface area.

The carbon nanotube produced with a vapor growth method or an arcelectric discharge method is known as the carbon fiber having a finefiber diameter. A fiber length of the carbon nanotube, however, isshort. For example, it is 10 μm or less. In addition, the carbonnanotube is expensive. Thus, an application of the carbon nanotube tothe electrode material causes a problem.

From such a background, the carbon fiber produced with a melt blowmethod or an electrospinning method has been proposed.

For example, the method of spinning thermoplastic containing a carbonsource (for example, pitch etc.) with the melt blow method, andthereafter, thermally decomposing, carbonizing and graphitizing theaforementioned thermoplastic has been proposed (Patent literature 1 andNon-patent literature 1). In accordance with this method, the carbonfiber having a fine fiber diameter is obtained. However, it is difficultto control the fiber diameter with the melt blow method. The carbonfiber obtained with the melt blow method is large in deviation of thefiber diameters

The method (the electrospinning method) of electrospinning a solutionhaving the carbon source (for example, a polymer such aspolyacrylonitrile) dissolved therein, and thereafter, carbonizing andgraphitizing it has been proposed (Patent literatures 2 to 5 andNon-patent literature 2). The carbon fiber obtained with this method issmall in deviation of the fiber diameters. However, in the methoddescribed in the above-mentioned Patent Literatures 2 to 5, the carbonsource has to be dissolved in a solvent. By the way, hard pitch andmesophase pitch are high in a graphitization degree. Thus, the hardpitch and the mesophase pitch are preferably employed as the carbonsource. However, the hard pitch and the mesophase pitch are notdissolved in the solvent. Thus, the hard pitch and the mesophase pitchare not employed as the carbon source in the above-mentioned PatentLiteratures. In the Patent literature 5, carbonization and thegraphitization are performed with microwave heating after theelectrospinning. Herein, carbon black is essential. The carbon black canbe employed as the carbon source. However, the carbon black, similarlyto polyacrylonitrile, is low in the graphitization degree. For thisreason, only the carbon fiber of which the graphitization degree is lowcan be obtained.

The technology of performing the electrospinning with the pitch kept ina molten state and thereafter, carbonizing and graphitizing it has beenproposed (Patent literature 6).

The carbon fiber obtained with this method is small in deviation of thefiber diameters. And yet, the graphitization degree is high. However,only the carbon source of which the graphitization degree is high isemployed in this technology, differently from the above-mentionedtechnologies. For this reason, shrinkage is small at the time of thecarbonization and the graphitization. Thus, it is difficult to obtainthe carbon fiber of which the fiber diameter is 1 μm or less. Inaddition, only soft pitch of which a melting point is 300° C. or loweris employed in the technology of the Patent literature 6. That is, thehigh pitch and the mesophase pitch of which the melting point is 300° C.or higher cannot be used. In principle, only the carbon fiber of whichthe surface is flat can be obtained in this method. That is, the carbonfiber having the characteristics of the present invention cannot beobtained.

CITATION LIST Non-Patent Literature

-   NPL 1: H. Ono, A. Oya/Carbon 44 (2006) 682-686-   NP12: Chan Kim, KapSeung Yang, Masahito Kojima, Kazuto Yoshida,    YongJung Kim, Yoong AhmKim and Morinobu Endo/Adv. Funct. Mater    16 (2006) 2393-2397-   NPL 3: Shirai Sousi/Carbon 240 (2009) 250-252

Patent Literature

-   PTL 1: JP-P2009-079346A-   PTL 2: JP-P2009-505931A-   PTL 3: JP-P2008-270807A-   PTL 4: JP-P2007-207654A-   PTL 5: JP-P2006-054636A1-   PTL 6: JP-P2009-203565A

SUMMARY OF INVENTION Technical Problem

A task that the present invention is to solve, that is, an object of thepresent invention is to provide the carbon fiber (or the nonwoven fabricconfigured of the aforementioned carbon fiber) of which a surface area,a graphitization degree, a fiber diameter are large, high, and small,respectively, and yet of which deviation is small.

Solution to Problem

The aforementioned problems are solved by a method of producing carbonfiber nonwoven fabric, which is characterized in including a dispersionliquid preparing step of preparing a dispersion liquid containing resinand pitch, an electrospinning step of producing the nonwoven fabriccomprised of carbon fiber precursors with electrospinning from theaforementioned dispersion liquid, and a modifying step of modifying thecarbon fiber precursors of the nonwoven fabric obtained in theaforementioned electrospinning step into the carbon fiber.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned modifying step includes a stepof heating the nonwoven fabric obtained in the aforementionedelectrospinning step to 50 to 4000° C.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned modifying step includes a resinremoving step of removing resin being included in the nonwoven fabricobtained in the aforementioned electrospinning step.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned resin removing step is aheating step of heating the nonwoven fabric obtained in theaforementioned electrospinning step under an oxidizing gas atmosphere.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned modifying step includes acarbonizing step of performing a carbonizing process for the nonwovenfabric subjected to the aforementioned resin removing step.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned modifying step includes agraphitizing step of performing a graphitizing process for the nonwovenfabric subjected to the aforementioned carbonizing step.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned graphitizing step is a heatingstep of heating the aforementioned nonwoven fabric under an inertatmosphere.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned heating is heat generation dueto electric current to the aforementioned nonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned resin is water-soluble resin.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned resin is pyrolytic resin.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned resin is polyvinyl alcohol.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that the aforementioned pitch is mesophase pitch.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that of the aforementioned pitch has a particlediameter of 1 nm to 10 μm.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that aforementioned pitch has a particle diameter of100 nm to 1 μm.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that an amount of the aforementioned pitch is 20 to 200parts by mass per 100 parts by mass of the aforementioned resin.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber nonwoven fabric, which ischaracterized in that an amount of the aforementioned pitch is 70 to 150parts by mass per 100 parts by mass of the aforementioned resin.

The aforementioned problems are solved by a method of producing carbonfiber, which is characterized in including a fabric unraveling step ofobtaining the carbon fiber by unraveling the carbon fiber nonwovenfabric obtained by the aforementioned method of producing the carbonfiber nonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedmethod of producing the carbon fiber, which is characterized in that theaforementioned fabric unraveling step is a step of pulverizing theaforementioned nonwoven fabric.

The aforementioned problems are solved by the carbon fiber obtained bythe aforementioned method of producing the carbon fiber.

The aforementioned problems are solved by the carbon fiber, which ischaracterized in that the aforementioned carbon fiber includes a largediameter portion and a small diameter portion, a diameter of theaforementioned large diameter portion is 20 nm to 2 μm, a diameter ofthe aforementioned small diameter portion is 10 nm to 1 μm, and (thediameter in the aforementioned large diameter portion)>(the diameter inthe aforementioned small diameter portion).

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that (a maximum value of thediameter in the aforementioned large diameter portion)/(a minimum valueof the diameter in the aforementioned small diameter portion) is 1.1 to100.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that a length of theaforementioned small diameter portion is longer than a minimum value ofthe diameter in the aforementioned large diameter portion.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that the length of theaforementioned small diameter portion is shorter than the maximum valueof the diameter in the aforementioned large diameter portion.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that the length of theaforementioned small diameter portion is 10 nm to 10 μm.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that the length of theaforementioned large diameter portion is 50 nm to 10 μm.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that the aforementioned carbonfiber includes the aforementioned large diameter portions in pluralnumber and yet the aforementioned small diameter portions in pluralnumber, and a length of the aforementioned carbon fiber is 0.1 to 1000μm.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that a specific surface area ofthe aforementioned carbon fiber is 1 m²/g to 100 m²/g.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that a peak originating in agraphite structure (002) exists within a range of 25° to 30° (2θ) in anX-ray diffraction measurement of the aforementioned carbon fiber, and ahalf width of the aforementioned peak is 0.1° to 2° (2θ).

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that ID/IG (ID is a peakintensity existing within 1300 cm⁻¹ to 1400 cm⁻¹ in Raman scatteringspectra of the aforementioned carbon fiber. IG is a peak intensityexisting within 1580 cm⁻¹ to 1620 cm⁻¹ in Raman scattering spectra ofthe aforementioned carbon fiber.) of the aforementioned carbon fiber is0.2 to 2.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is characterized in that L/(S)^(1/2) (S is an areaof the aforementioned carbon fiber in an image obtained by observing theaforementioned carbon fiber with a scanning electron microscope. L is anouter length of the aforementioned carbon fiber in the image obtained byobserving the aforementioned carbon fiber with the scanning electronmicroscope.) of the aforementioned carbon fiber is 3.7 to 300.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber, which is obtained with the aforementioned method ofproducing the carbon fiber.

The aforementioned problems are solved by carbon fiber nonwoven fabric,which is characterized in that a containing ratio of the aforementionedcarbon fiber is 50 to 100% by mass.

The aforementioned problems are solved by carbon fiber nonwoven fabric,which is obtained with the aforementioned method of producing the carbonfiber nonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber nonwoven fabric, which is characterized in that a thicknessof the aforementioned nonwoven fabric is 0.1 μm to 10 mm.

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber nonwoven fabric, which is characterized in that a weight ofthe aforementioned nonwoven fabric is 0.1 to 10000 g/m².

Preferably, the aforementioned problems are solved by the aforementionedcarbon fiber nonwoven fabric, which is characterized in that a specificsurface area of the aforementioned nonwoven fabric is 1 to 50 m²/g.

The aforementioned problems are solved by a member to be employed forelectric devices, which is characterized in being configured byemploying the aforementioned carbon fiber or the aforementioned carbonfiber nonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which is characterized inbeing a battery part.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which is characterized inbeing an electrode of a battery.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which is characterized inbeing an electrode of a lithium-ion secondary battery.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which is characterized inbeing a negative electrode of a lithium-ion secondary battery, andcontaining an anode active material that is comprised of theaforementioned carbon fiber and/or the aforementioned carbon fibernonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedmember being employed for electric devices, which is characterized inbeing an electrode of a lithium-ion secondary battery and including aconductive auxiliary that is comprised of the aforementioned carbonfiber and/or the aforementioned carbon fiber nonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedmember being employed for electric devices, which is characterized inthat the aforementioned member is a negative electrode of a lithium-ionsecondary battery employing an alloy-based anode active material, andthe aforementioned alloy-based anode active material is laminated on theaforementioned carbon fiber and/or the aforementioned carbon fibernonwoven fabric.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which are characterized inbeing an electrode of a capacitor.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which is characterized inbeing an electrode of a lithium-ion capacitor.

Preferably, the aforementioned problems are solved by the aforementionedmember to be employed for electric devices, which is characterized inbeing a porous carbon electrode material for fuel cells.

The aforementioned problems are solved by an electric devise, which ischaracterized in including the member to be employed for an electricelement.

The aforementioned problems are solved by a filter, which is configuredby employing the aforementioned carbon fiber or the aforementionedcarbon fiber nonwoven fabric.

Advantageous Effect of Invention

The carbon fiber of which the surface area and the graphitization degreeand the fiber diameter are large, high and small, respectively, and yetof which deviation is few can be obtained.

The carbon fiber nonwoven fabric having the aforementioned features canbe obtained in a simplified manner. The surface area of the abovenonwoven fabric is large.

The carbon fiber and the nonwoven fabric having the aforementionedfeatures are suitable, for example, for the electrode materials. Inparticular, a speed at which the electrolyte solution is poured is highbecause the surface area is large, and thus, a takt time can beshortened.

The carbon fiber having the aforementioned features is large in anaspect ratio and high in conductivity. Thus, employing the conductiveauxiliary leads to a reduction in an internal resistance of the battery.

The carbon fiber and the nonwoven fabric having the aforementionedfeatures can be employed, for example, for the filters.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of the electrospinning apparatus.

FIG. 2 is a schematic view of the electrospinning apparatus.

FIG. 3 is a schematic view of the negative electrode of the lithium-ionbattery.

FIG. 4 is a schematic view of the negative electrode of the lithium-ioncapacitor.

FIG. 5 is an SEM photograph.

FIG. 6 is an XRD chart.

FIG. 7 is Raman scattering spectra.

FIG. 8 is an image obtained by processing the image employed formeasuring L/(S)^(1/2).

FIG. 9 is an SEM photograph.

FIG. 10 is an image obtained by processing the image employed formeasuring L/(S)^(1/2).

FIG. 11 is an SEM photograph.

FIG. 12 is an SEM photograph.

FIG. 13 is an image obtained by processing the image employed formeasuring L/(S)^(1/2).

FIG. 14 is an SEM photograph.

FIG. 15 is an SEM photograph.

FIG. 16 is an SEM photograph.

FIG. 17 is a charge/discharge characteristic chart.

FIG. 18 is a charge/discharge characteristic chart.

FIG. 19 is an SEM photograph.

FIG. 20 is an SEM photograph.

FIG. 21 is a charge/discharge characteristic chart.

FIG. 22 is a charge/discharge characteristic chart.

FIG. 23 is a cross-sectional view of an anode electrode.

FIG. 24 is an SEM photograph.

FIG. 25 is an energy density/output density characteristic chart.

DESCRIPTION OF EMBODIMENTS

A first invention is a method of producing the carbon fiber nonwovenfabric. The aforementioned producing method includes a dispersion liquidpreparation step. This dispersion liquid preparation step is a step ofpreparing a dispersion liquid containing resin and pitch (carbonparticles). The aforementioned producing method includes anelectrospinning step. This electrospinning step is a step ofelectrospinning the aforementioned dispersion liquid. Thiselectrospinning step allows the nonwoven fabric that is comprised ofcarbon fiber precursors to be produced. The aforementioned producingmethod includes a modifying step. This modifying step is a step ofmodifying the carbon fiber precursors of the nonwoven fabric obtained inthe aforementioned electrospinning step into the carbon fiber.

The aforementioned modifying step includes a heating step. In thisheating step, the aforementioned nonwoven fabric (the nonwoven fabricmade of the carbon fiber precursors) is heated, for example, to 50 to4000° C.

The aforementioned modifying step preferably includes a resin removingstep. This resin removing step is a step of removing resin beingincluded in the nonwoven fabric obtained in the aforementionedelectrospinning step. The aforementioned resin removing step is, forexample, a heating step. This heating step is a step of heating thenonwoven fabric (the nonwoven fabric obtained in the aforementionedelectrospinning step), for example, under an oxidizing gas atmosphere.The aforementioned modifying step preferably includes a carbonizingstep. This carbonizing step is a step of performing a carbonizingprocess for the nonwoven fabric (in particular, the nonwoven fabricsubjected to the aforementioned resin removing step). The aforementionedmodifying step preferably includes a graphitizing step. Thisgraphitizing step is a step of performing a graphitizing process for thenonwoven fabric (in particular, the nonwoven fabric subjected to theaforementioned carbonizing step). The aforementioned graphitizing stepis, for example, a heating step. This heating step is a step of heatingthe nonwoven fabric (in particular, the nonwoven fabric subjected to theaforementioned carbonizing step), for example, under an inertatmosphere. The aforementioned heating step is, for example, a heatgenerating step due to electric current to the nonwoven fabric (inparticular, the nonwoven fabric subjected to the aforementionedcarbonizing step).

The aforementioned resin is preferably is water-soluble resin. Theaforementioned resin is preferably pyrolytic resin. In particular, theaforementioned resin is preferably water-soluble and yet pyrolyticresin. The most preferable resin is polyvinyl alcohol. Theaforementioned carbon particles are pitch. The aforementioned pitch ispreferably hard pitch or mesophase pitch. The most preferable pitch isthe mesophase pitch. (An amount of the aforementioned pitch)/(an amountof the aforementioned resin) is preferably 0.2 to 2 (more preferably,0.7 to 1.5) (mass ratio).

A second invention is a method of producing the carbon fiber. Thismethod of producing the carbon fiber includes a fabric unraveling step.This fabric unraveling step is a step of unraveling the aforementionednonwoven fabric (the carbon fiber nonwoven fabric obtained in theaforementioned first invention (the aforementioned method of producingthe carbon fiber nonwoven fabric)). The aforementioned fabric unravelingstep is, for example, a step of pulverizing the nonwoven fabric. Thecarbon fiber is obtained by the aforementioned fabric unraveling step.

A third invention is the carbon fiber. This carbon fiber includes alarge diameter portion and a small diameter portion. The aforementionedlarge diameter portion is a portion having a large diameter. Theaforementioned small diameter portion is a portion having a smalldiameter. The aforementioned carbon fiber preferably includes theaforementioned large diameter portions in plural number. Theaforementioned carbon fiber preferably includes the aforementioned smalldiameter portions in plural number. A diameter of the aforementionedlarge diameter portion is preferably 20 nm to 5 μm (yet preferably, 20nm to 2 μm (more preferably, 50 nm to 1 μm)). A diameter of theaforementioned small diameter portion is preferably 10 nm to 3 μm (yetpreferably, 10 nm to 1 μm (more preferably, 20 to 500 nm)). Needless tosay, a condition A [(the diameter (an averaged value of the diameters)in the aforementioned large diameter portion)>(the diameter (an averagedvalue of the diameters) in the aforementioned small diameter portion)]is satisfied. Preferably, a condition B [(a maximum value of thediameter in the aforementioned large diameter portion)/(a minimum valueof the diameter in the aforementioned small diameter portion)=1.1 to100] is satisfied. Yet preferably, a condition C [(a maximum value ofthe diameter in the aforementioned large diameter portion)/(a minimumvalue of the diameter in the aforementioned small diameter portion)=2 to50] is satisfied. A length of the aforementioned small diameter portionis, for example, longer than a minimum value of the diameter in theaforementioned large diameter portion. The length of the aforementionedsmall diameter portion is, for example, shorter than a maximum value ofthe diameter in the aforementioned large diameter portion. The length ofthe aforementioned small diameter portion is preferably 10 nm to 10 μm(more preferably, 50 nm to 1 μm). The length of the aforementioned largediameter portion is preferably 50 nm to 10 μm (more preferably, 500 nmto 3 μm). The length (full length) of the aforementioned carbon fiber ispreferably 0.1 to 1000 μm (more preferably, 10 to 500 μm, and 0.5 to 10μm in a case where the crushed carbon fiber is employed). A specificsurface area of the aforementioned carbon fiber is preferably 1 to 100m²/g (more preferably, 2 to 50 m²/g). A peak originating in a graphitestructure (002) exists preferably within a range of 25° to 30° (2θ) inan X-ray diffraction measurement of the aforementioned carbon fiber. Ahalf width of the aforementioned peak is 0.1° to 2°. The aforementionedcarbon fiber preferably satisfies a condition D [ID/IG=0.1 to 2]. Theaforementioned ID is a peak intensity existing within a range of 1300cm⁻¹ to 1400 cm⁻¹ in Raman scattering spectra of the aforementionedcarbon fiber. The aforementioned IG is a peak intensity existing withina range of 1580 cm⁻¹ to 1620 cm⁻¹ in Raman scattering spectra of theaforementioned carbon fiber. An Ar⁺ laser is preferable as an excitationsource to be employed at the time of the measurement. The aforementionedcarbon fiber preferably satisfies a condition E [L/(S)^(1/2)=2 to 300,preferably, 5 to 300]. The aforementioned S is an area of theaforementioned carbon fiber in an image obtained by observing theaforementioned carbon fiber with a scanning electron microscope. Theaforementioned L is an outer length of the aforementioned carbon fiberin the image obtained by observing the aforementioned carbon fiber withthe scanning electron microscope. The carbon fiber of this feature isobtained with the aforementioned method of producing the carbon fiber(the preferable method of producing the carbon fiber).

A fourth invention is the carbon fiber nonwoven fabric. With regard tothe above nonwoven fabric, a containing ratio of the aforementionedcarbon fiber is preferably 50 to 100% by mass (more preferably, 80% ormore by mass). The aforementioned nonwoven fabric is the nonwoven fabricobtained by the aforementioned first invention (the aforementionedmethod of producing the nonwoven fabric of the carbon fiber). Athickness of the aforementioned nonwoven fabric is preferably 0.1 μm to10 mm (more preferably, 10 to 500 μm). A weight of the aforementionednonwoven fabric is preferably 1 to 10000 g/m² (more preferably, 10 to1000 g/m²). A specific surface area of the aforementioned nonwovenfabric is preferably, 1 to 50 m²/g (more preferably, 2 to 30 m²/g).

A fifth invention is the electrode of the battery. This electrode isconfigured of the aforementioned carbon fiber (or the aforementionedcarbon fiber nonwoven fabric). The aforementioned battery is, forexample, a lithium-ion secondary battery. The aforementioned battery is,for example, a capacitor (an electric double-layer capacitor). Theaforementioned capacitor is, for example, a lithium-ion capacitor.

A sixth invention is the battery. This battery is provided with theaforementioned electrodes.

A seventh invention is the filter. This filter is configured of theaforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber).

Hereinafter, the present invention will be explained more detailedly.

[The Dispersion Liquid Preparing Step (Step I)]

The aforementioned dispersion liquid contains the resin and the carbonparticles.

The aforementioned resin is preferably resin that is dissolved in asolvent (a solvent that is volatilized at the time of theelectrospinning). Specifically, the aforementioned resin is vinyl resin(for example, polyvinyl alcohol (PVA), polyvinylbutyral (PVB), and thelike). Or the aforementioned resin is polyethylene oxide (PEO). Or theaforementioned resin is acrylic resin (for example, polyacrylic acid(PAA), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), and thelike). Or, the aforementioned resin is fluorine resin (for example,polyvinylidene difluoride (PVDF), and the like). Or, the aforementionedresin is polymer from natural products (for example, cellulose resin andits derivatives (poly-lactic acid, chitosan, carboxymethylcellulose(CMC), hydroxyethylcellulose (HEC), and the like). Or, theaforementioned resin is engineering plastic resin such aspolyethersulfone (PES). Or, the aforementioned resin is polyurethanerasin (PU). Or, the aforementioned resin is polyamide resin (nylon). Or,the aforementioned resin is aromatic polyamide resin (aramid resin). Or,the aforementioned resin is polyester resin. Or, the aforementionedresin is polystyrene resin. Or, the aforementioned resin ispolycarbonate resin. Or, the aforementioned resin is a mixture or acopolymer of the aforementioned resin.

The aforementioned resin is preferably water-soluble resin from aviewpoint of a countermeasure for VOC (volatile organic compounds). Theaforementioned resin is, for example, polyvinyl alcohol (PVA),polyvinylbutyral (PVB), polyethylene oxide (PEO), polyacrylic acid(PAA), or cellulose derivatives.

The preferable fiber is fiber of which fusion and bonding do not occurin the aforementioned resin removing step (the thermal treating step:the heating step). Preferably, the aforementioned resin is pyrolyticresin from this viewpoint. The pyrolytic resin is resin that isthermally decomposed before thermal deformation (fusion and bonding)when the resin is heated. The pyrolytic resin is, for example, polyvinylalcohol, cellulose derivatives, polyacrylic acid (PAA) or whollyaromatic polyamide resin (aramid resin).

The aforementioned resin is preferably polyvinyl alcohol, cellulosederivatives or polyacrylic acid (PAA). The particularly preferable resinis polyvinyl alcohol.

The aforementioned solvent is preferably a solvent that is volatilizedat the time of the electrospinning. The aforementioned solvent is, forexample, water. Or the aforementioned solvent is acid (acetic acid,formic acid, and the like). Or the aforementioned solvent is alcohol(for example, methanol, ethanol, propanol, butanol, isobutyl alcohol,amyl alcohol, isoamyl alcohol and cyclohexanol). Or the aforementionedsolvent is ester (for example, ethyl acetate and butyl acetate). Or theaforementioned solvent is ether (for example, diethyl ether, dibutylether and tetrahydrofuran). Or the aforementioned solvent is ketone(acetone, methyl ethyl ketone, methyl isobutyl ketone, and the like). Orthe aforementioned solvent is an aprotic polar solvent (for example,N,N′-dimethyl formamide, dimethyl sulfoxide, acetonitrile and dimethylacetamide). Or the aforementioned solvent is halogenated hydrocarbon(for example, chloroform, tetrachloromethane and hexafluoroisopropylalcohol). Or the aforementioned solvent is a mixture of theaforementioned compounds.

The preferable solvent is water, alcohol or a mixture thereof from aviewpoint of a countermeasure for VOC (volatile organic compounds). Theparticularly preferable solvent is water.

For example, carbon black, fullerene and carbon nanotubes are known asthe carbon particles. The carbon particles that are employed in thisstep 1 are pitch. The preferable pitch is the hard pitch or themesophase pitch. The particularly preferable pitch is the mesophasepitch. In the present invention, the carbon particles other than thepitch are used together with the pitch. The pitch is substantiallycomprised of only carbon. The pitch is not dissolved in theaforementioned solvent. A fixed carbon content of the aforementionedmesophase pitch is preferably 50 to 100% (more preferably, 70 to 95% andyet more preferably, 80 to 90%). A melting point of the aforementionedmesophase pitch is preferably 250 to 400° C. (more preferably, 280 to350° C. and yet more preferably, 300 to 330° C.). A particle diameter ofthe aforementioned carbon particles (a particle diameter of the carbonparticles in the dispersion liquid) is preferably 10 to 1000 nm (morepreferably, 50 nm or more, yet more preferably, 100 nm or more, morepreferably, 500 nm or less, and yet more preferably, 300 nm or less).

The aforementioned pitch dispersion liquid includes carbon nanotubesresponding to a necessity from a viewpoint of the strength andconductivity. The carbon nanotube is, for example, a single-walledcarbon nanotube (SWNT). Or the carbon nanotube is, for example, amulti-walled carbon nanotube (MWNT). Or the carbon nanotube is a mixturethereof. The multi-walled carbon nanotube (MWNT) is employed from aviewpoint of practical use. As a method of incorporating the carbonnanotubes, the method is employed of adding carbon nanotube powders (orcarbon nanotube dispersion liquid) to the pitch dispersion liquid. Theaforementioned carbon nanotube dispersion liquid and the aforementionedpitch dispersion liquid are preferably mixed. An amount of theaforementioned carbon nanotubes is preferably 0.01 to 10 parts by mass(more preferably, 0.1 to 1 part by mass) per 100 parts by mass of theaforementioned pitch.

The aforementioned pitch (carbon particles) dispersion liquid includes agraphitization promoter responding to a necessity. The graphitizationpromoter is a catalyst having an effect of promoting the graphitizationdegree. The aforementioned graphitization promoter is, for example,borons (for example, boron, boric ester, boron carbide, and the like),or silicons (for example, silicon, silicic ester, silicon carbide, andthe like). The preferable graphitization promoter is boron carbide orsilicon carbide. An amount of the aforementioned graphitization promoteris preferably 1 to 10000 ppm by mass for the carbon particles (morepreferable, 10 to 1000 ppm by mass). The aforementioned graphitizationpromoter and the aforementioned pitch dispersion liquid are mixed whenthe aforementioned graphitization promoter is liquid. At first, thedispersion liquid of the graphitization promoter is prepared when theaforementioned graphitization promoter is powders. And, the abovedispersion liquid and the aforementioned pitch dispersion liquid aremixed.

The aforementioned pitch dispersion liquid includes a dispersantresponding to a necessity. The aforementioned dispersant is, forexample, a surfactant or a polymer. An amount of the aforementioneddispersant is preferably 1 to 200 parts by mass (more preferably, 10 to100 parts by mass) per 100 parts by mass of the pitch.

A ratio of the aforementioned resin and the aforementioned pitch ispreferably the following ratio. When the aforementioned resin is toomuch, the remaining carbon content after the carbonization becomes few.Contrarily, when the aforementioned resin is too few, theelectrospinning becomes difficult. Thus, an amount of the aforementionedpitch is preferably 20 to 200 parts by mass (more preferably, 30 to 150parts by mass) per 100 parts by mass of the aforementioned resin. Whenthe carbon fiber having the aforementioned large diameter portion andthe aforementioned small diameter portion should be acquired, an amountof the aforementioned pitch is preferably 50 to 200 parts by mass (morepreferably, 70 to 150 parts by mass) per 100 parts by mass of theaforementioned resin.

When a density of solid (components other than the solvent) in theaforementioned dispersion liquid is too high, the spinning is difficult.Contrarily, also when the aforementioned density is too law, thespinning is difficult. Thus, a density of the aforementioned solid ispreferably 0.1 to 50% by mass (more preferably, 1 to 30% by mass and yetmore preferably, 5 to 20% by mass).

When a viscosity of the aforementioned dispersion liquid is too high,drawability is lacking at the time of the spinning. Contrarily, when theaforementioned viscosity is too law, the spinning is difficult. Thus,the viscosity of the aforementioned dispersion liquid (the viscosity atthe time of the spinning: the viscosity measuring instrument is acoaxial double-cylindrical viscometer) is preferably 10 to 10000 mPa·S(more preferably, 50 to 5000 mPa·S and yet more preferably, 500 to 5000mPa·S).

The preparation of the aforementioned dispersion liquid includes amixing step and a refining step. The aforementioned mixing step is astep of mixing the aforementioned resin and the aforementioned pitch.The aforementioned refining step is a step of refining theaforementioned pitch. The aforementioned refining step is, for example,a step of affixing shear strength to the aforementioned pitch. Thisallows the pitch to be refined. It doesn't matter which step, out of themixing step and the refining step, is firstly performed. They may besimultaneously performed.

In the aforementioned mixing step, there are three cases, namely, thecase in which each of the aforementioned resin and the aforementionedpitch is powders, the case in which one is powders, and the other is asolution (dispersion liquid), and the case in which each of theaforementioned resin and the aforementioned pitch is a solution(dispersion liquid). The preferable case is that each of theaforementioned resin and the aforementioned pitch is a solution(dispersion liquid) from a viewpoint of operability.

In the aforementioned refining step, for example, a medialess beads millis employed. Or a beads mill is employed. Or an ultrasound irradiationmachine is employed. When foreign materials should be prevented frommixedly entering, the medialess beads mill is preferably employed. Whena particle diameter of the carbon particles should be controlled, thebeads mill is preferably employed. When the refining step should beperformed in a simple operation, the ultrasound irradiation machine ispreferably employed. In the present invention, the beads mill ispreferably employed because a control of the particle diameter of thepitch (carbon particles) is important.

In the aforementioned dispersion liquid, when the particle diameter ofthe aforementioned pitch is too large, the fiber diameter becomes toolarge. When the particle diameter of the aforementioned pitch is toosmall, the dispersion condition becomes unstable. Thus, theaforementioned particle diameter is preferably 1 nm to 10 μm (morepreferably, 10 nm to 1 μm).

[The Electrospinning Step (Step of Producing the Nonwoven Fabric that isComprised of the Carbon Fiber Precursors) (Step II)]

The electrospinning apparatus is employed in this step.

For example, the electrospinning apparatus of FIG. 1 is employed. InFIG. 1, 1 is a pump-type spinning dope supplying apparatus. 2 is anozzle-type exit. 3 is a voltage applying apparatus. 4 is a collector.The collector 4 is earthed. The aforementioned dispersion liquid(spinning dope) is forced to scatter toward the collector 4 from theexit 2. The solvent is volatilized at the time of this scattering. Thespinning dope coming from the exit 2 is subjected to a drawing operationdue to an electromagnetic field (the electromagnetic field applied bythe voltage applying apparatus 3 (the electromagnetic field between theexit 2 and the collector 4)). The spinning dope arrives at the collector4 while its solvent is volatilized. At a time point that the spinningdope arrives at the collector 4, it becomes fibrous (it is in afiber-shape in which the solvent has been removed). The above fibroussubstances, which are accumulated (deposited), become the nonwovenfabric.

The spinning dope supplying apparatus is not limited to the apparatus ofFIG. 1. The spinning dope supplying apparatus 1 is, for example, asyringe pump, a tube pump or a dispenser. The spinning dope supplyingapparatus could be a pan-type spinning dope supplying apparatus (seeFIG. 2, 5: a pan-type spinning dope supplying apparatus and 6: adrum-type exit). An inner diameter of the exit is 0.1 to 5 mm(preferably, 0.5 to 2 mm) when the exit has a nozzle shape. The exit ismade of metal or non-metal. A waistline of the exit is flat-shaped orwire-shaped in the case of the drum type. The exit is made of metal inthe case of the drum type.

The aforementioned voltage applying apparatus 3 is, for example, a DChigh-voltage generator. Or the aforementioned voltage applying apparatus3 is a Van de Graaff generator. The preferable applying voltage is 5 to50 kV or so when the nozzle-type exit is employed. The preferableapplying voltage is 10 to 200 kV or so when the drum-type exit isemployed.

The aforementioned electromagnetic field strength is, for example, 0.1to 5 kV/cm. When the electromagnetic field strength exceeds 5 kV/cm,breakdown of air easily occurs. When the electromagnetic field strengthis small, namely, less than 0.1 kV/cm, the drawablility of the spinningdope is insufficient. For this, fiberization is difficult.

The aforementioned collector 4 is a confrontation-electrode typecollector. However, the aforementioned collector is not aconfrontation-electrode type collector in some cases. That is, when thecollector is arranged between the exit and the confrontation electrode,the above collector is not a confrontation-electrode type collector.When the collector 4 is a confrontation-electrode type collector, thecollector 4 is preferably configured of conductive materials (forexample, metal) of which a volume resistivity is 10 E9 Ω·m or lower. Thecollector is configured of, for example, the nonwoven fabric. Or thecollector is configured of fabric, knitted fabric, nets, flat plates,belts or the like. The collector is configured of liquid such as waterand organic solvents in some cases. A configuration thereof assumes apiece by piece system in some cases, and assumes a roll-to-rollcontinuous system in some cases. The continuous operation type collector4 is preferably employed from a viewpoint of production efficiency.

When a distance between the exit 2 and the collector 4 is too short, thesolvent is not volatilized. When the aforementioned distance is toolong, the voltage necessary is raised. The preferable distance is 5 cmto 1 m. The more preferable distance is 10 to 70 cm.

The nonwoven fabric obtained in this step is configured of the carbonfiber precursors. The carbon fiber precursors are a mixture of resin notsubjected to the thermal treatment and the carbon particles (pitch). Theaforementioned nonwoven fabric has a suitable thickness from a viewpointof operability. A thickness of the nonwoven fabric after thecarbonization (graphitization) is preferably 0.1 μm to 10 mm (morepreferably, 1 μm or more, yet more preferably, 10 μm or more, morepreferably, 1 mm or less and yet more preferably, 500 m or less). Aweight of the nonwoven fabric after the carbonization is preferably 1 to1000 g/m² (more preferably, 10 to 500 g/m²).

With the carbon fiber having irregularity (the carbon fiber having thelarge diameter portion (the portion in which the diameter of the carbonfiber is large) and the small diameter portion (the portion in which thediameter of the carbon fiber is small)), the features of the presentinvention are largely exhibited. When the surface of the carbon fiber isirregularly shaped, a surface area of the above carbon fiber is large.As a result, the features of the present invention are largelyexhibited. The aforementioned fiber is preferably a fiber having thefollowing size. The diameter of the aforementioned small diameterportion after the carbonization (graphitization) was preferably 10 nm to1 μm (more preferably, 20 nm or more and more preferably, 500 nm orless). The diameter of the aforementioned large diameter portion afterthe carbonization (graphitization) was preferably 20 nm to 2 μm (morepreferably, 50 nm or more, yet more preferably, 100 nm or more, morepreferably, 1.5 μm or less and yet more preferably, 1 μm or less).Needless to say, the condition [(the diameter (an averaged value of thediameters) in the aforementioned large diameter portion)>(the diameter(an averaged value of the diameters) in the aforementioned smalldiameter portion)] is satisfied. It was when [(a maximum value of thediameter in the aforementioned large diameter portion)/(a minimum valueof the diameter in the aforementioned small diameter portion)]=1.1 to100 (more preferably, 2 or more, more preferably, 50 or less, and yetmore preferably, 20 or less) that an effect for which the presentinvention aimed was largely exhibited. When the aforementioned largediameter portion became too large, the aforementioned fiber was easilycut off. When the aforementioned large diameter portion became toosmall, the effect for which the present invention aimed was small. Thelength of the aforementioned small diameter portion after thecarbonization (graphitization) was preferably 10 nm to 10 μm (morepreferably, 50 nm to 1 μm). The effect for which the present inventionaimed was small also when the length of the aforementioned smalldiameter portion was too short and too long. The length of theaforementioned large diameter portion after the carbonization(graphitization) was preferably 50 nm to 10 μm (more preferably, 500 nmto 3 μm). The effect for which the present invention aimed was smallalso when the length of the aforementioned large diameter portion wastoo short and too long. The length of the aforementioned carbon fiber (afull length of one fiber) after the carbonization (graphitization) waspreferably 0.1 to 1000 μm (more preferably, 10 to 500 μm, and 0.5 to 10μm in the case that the carbon fiber was pulverized and employed). Theeffect for which the present invention aimed was small when the lengthof the aforementioned fiber was too short.

The specific surface area (BET specific surface area) of theaforementioned carbon fiber after the carbonization (graphitization) waspreferably 1 to 100 m²/g (more preferably, 2 to 50 m²/g).

The peak originating in a graphite structure (002) of the aforementionedcarbon fiber after the carbonization (graphitization) preferably existswithin a range of 25° to 30° (2θ) in an X-ray diffraction measurementthereof. A half width of the aforementioned peak is 0.1° to 2° (morepreferably, 0.1° to 1°). Crystallinity of the graphite is inferior whenthe aforementioned half width is too large. When the above carbon fiberwas employed as the battery, performance thereof was inferior.

The aforementioned carbon fiber after the carbonization (graphitization)preferably satisfy the condition D [ID/IG=0.1 to 2]. More preferably,the aforementioned ratio is 0.1 to 1. The crystallinity of the graphiteis inferior when the aforementioned ratio is too large. When the abovecarbon fiber was employed as the battery, performance thereof wasinferior.

The aforementioned carbon fiber preferably satisfy the condition E[L/(S)^(1/2)=5 to 300]. More preferably, the aforementioned ratio was 50to 200. The number of the fiber that enters a measurement range when theSEM observation is made is preferably 50 or more. That is, when thenumber of the fiber was 50 or more, a measurement error was small. Aname of a program under which this operational processing was performedis “imageJ” (US National Institute of Mental Health/National Instituteof Neurological Disorders and Stroke, Research Support Branch HPhttp://rsb.info.nih.gov/ij/index.html)

The carbon fiber constituting the nonwoven fabric of the presentinvention is preferably the carbon fiber having the aforementionedfeatures. However, the carbon fiber having no aforementioned featuresmay be incorporated. For example, the features of the present inventionwere not impaired so long as (an amount of the carbon fiber having thefeatures of the present invention)/(an amount of the carbon fiber havingthe features of the present invention+an amount of the carbon fiberhaving no features of the present invention)≧0.5 was satisfied.Preferably, the aforementioned ratio is 0.6 or more. More preferably,the aforementioned ratio is 0.7 or more. Yet more preferably, theaforementioned ratio is 0.8 or more. Most preferably, the aforementionedratio is 0.9 or more.

Plural sheets of the aforementioned nonwoven fabric made of the carbonfiber precursors may be laminated. The laminated nonwoven fabric may becompressed with the roll. That is, the compression allows the membranethickness and the density to be appropriately regulated.

The nonwoven fabric that is comprised of the carbon fiber precursors ispeeled off from the collector and treated. Or the aforementionednonwoven fabric is treated in a state of sticking to the collector.

[The Modifying Step (Step III)]

[The Thermal Treatment of the Aforementioned Nonwoven Fabric Made of theCarbon Fiber Precursors (Step III-1)]

The carbon fiber nonwoven fabric is obtained from the aforementionednonwoven fabric made of the carbon fiber precursors. This is obtained bymodifying the aforementioned carbon fiber precursors into the carbonfiber. The modifying process is, for example, a thermal treatment. Inparticular, the modifying process is a thermal treatment under theoxidative gas atmosphere. This thermal treatment allows the resinconstituting the aforementioned carbon fiber precursors to be removed.That is, the carbon sources other than the carbon particles are removed.Yet, curing of the aforementioned carbon particles is performed.

This step is preferably performed after the aforementionedelectrospinning step (the aforementioned step II).

The oxidative gas in this step is a compound containing oxygen atoms oran electron acceptor compound. The aforementioned oxidative gas is, forexample, air, oxygen, halogen gas, nitrogen dioxide, ozone, water vapor,or carbon dioxide. From among them, the preferable oxidative gas is airfrom a viewpoint of cost performance and quick curing at a lowtemperature. Or the preferable oxidative gas is gas containing halogengas. The aforementioned halogen gas is, for example, fluorine, iodineand bromine. From among them, the preferable halogen gas is iodine. Orthe preferable halogen gas is mixture gas of the aforementionedcomponents.

A temperature of the aforementioned thermal treatment is preferably 100to 400° C. (more preferably, 150 to 350° C.). A time of theaforementioned thermal treatment is preferably 3 minutes to 24 hours(more preferably, 5 minutes to 2 hours).

The cured nonwoven fabric made of the carbon fiber precursors isobtained in this step. A softening temperature of this cured carbonfiber precursors is preferably 400° C. or higher (more preferably, 500°C. or higher).

The aforementioned resin is subjected to a crystallization process priorto this step when the aforementioned resin is crystalline resin. Thatis, the aforementioned resin is preferably kept for approximately oneminute to one hour at a temperature equal to or more than a glasstransition temperature, and yet equal to or less than a melting point.The glass transition temperature of polyvinyl alcohol is approximately50 to 90° C., and the melting point thereof is 150 to 250° C.

This step is performed in a piece by piece system. Or this step isperformed in a roll-to-roll continuous system. Or the aforementionedresin is thermally treated in a state of the roll. The preferable stepis a roll-to-roll continuous thermal treatment process from a viewpointof production efficiency.

[The Carbonizing Process (Step III-2)]

The carbonizing process is preferably performed in order to obtain thecarbon fiber nonwoven fabric. This carbonizing process is a thermaltreatment. This carbonizing process is preferably a thermal treatmentunder an inert gas atmosphere. The aforementioned cured carbon fiberprecursors become the carbon fiber through this step. This step ispreferably performed after the aforementioned step III-1.

The inert gas in this step is gas that does not chemically react to thecured carbon fiber precursors during the carbonizing process. The inertgas is, for example, nitrogen, argon and krypton. From among them, thepreferable inert gas is nitrogen gas from a viewpoint of the cost.

A processing temperature of this step is preferably 500 to 2000° C.(more preferably, 600 to 1500° C.). The carbonization hardly progressesat a temperature less than 500° C. The graphitization occurs at atemperature exceeding 2000° C. However, when a graphitizing process tobe later described is performed, a rise in the temperature exceeding2000° C. is acceptable. A processing time of this step is preferably 5minute to 24 hours (more preferably, 30 minute to 2 hours).

[The Graphitizing Process (Step III-3)]

The graphitizing process is preferably performed. The graphitizingprocess is preferably performed under an inert gas atmosphere. This stepis an important step when the nonwoven fabric is employed for negativeelectrodes of the lithium-ion batteries and the like. This step ispreferably performed after the aforementioned step III-2.

The inert gas in this step is gas that does not chemically react to thecarbon fiber precursors during the graphitizing process. The inert gasis, for example, argon and krypton. Nitrogen gas is not preferablebecause it is ionized.

A processing temperature of this step is preferably 2000 to 3500° C.(more preferably, 2300 to 3200° C.). A processing time is preferably onehour or less (more preferably, 0.1 to 10 minutes).

This step is performed by keeping the carbon fiber precursors at theaforementioned temperature. In particular, the above step is performedby the electric current to the carbon fiber nonwoven fabric. That is,the aforementioned temperature is kept owing to Joule heat beinggenerated due to the electric current. Also microwave heating enablesthe graphitization. The preferable graphitizing process iselectric-current heating from a viewpoint of production cost. Inparticular, the continuous process using the roll-to-roll system ispreferably performed.

[The Fiberizing Process (Step IV)]

This step is a step of obtaining the carbon fiber from the nonwovenfabric obtained in the aforementioned step. This step is a step ofpulverizing the nonwoven fabric obtained, for example, by theaforementioned step II, the aforementioned step III-1, theaforementioned step III-2, or the aforementioned step III-3. Preferably,this step is a step of pulverizing the nonwoven fabric obtained by theaforementioned step III-2 and the aforementioned step III-3. Pulverizingthe nonwoven fabric allows the fiber to be obtained.

For example, a cutter mill, a hammer mill, a pin mill, a ball mill, or ajet mill is employed for pulverizing the nonwoven fabric. Any method ofthe wet method and the dry method can be adopted. However, the drymethod is preferably employed when the fiber is employed for a fieldsuch as nonaqueous electrolyte secondary batteries.

[The Electrodes]

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is employed for the members of the electric elements (theelectronic elements are also included in the electric elements). Forexample, the aforementioned carbon fiber nonwoven fabric (or theaforementioned carbon fiber) is employed for the members of thebatteries, the capacitors, the fuel cells and the like.

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is applied for the electrodes of the batteries. Thebatteries are, for example, a lead battery, a nickel-cadmium battery, anickel-hydrogen battery, a lithium-ion battery, a sodium-sulfur batteryand a redox flow battery. From among them, the carbon fiber nonwovenfabric (or the aforementioned carbon fiber) is applied for theelectrodes of the lithium-ion battery. The aforementioned electrode ispreferably a negative electrode. The aforementioned carbon fibernonwoven fabric (or the aforementioned carbon fiber) is preferablyapplied to an anode active material. The aforementioned carbon fibernonwoven fabric (or the aforementioned carbon fiber) is preferablyapplied to a conductant agent.

The lithium-ion battery is comprised of members such as positiveelectrodes, negative electrodes, separators, and an electrolytesolution. The positive electrode and the negative electrode areconfigured as follows. That is, the positive electrode and the negativeelectrode are configured by laminating a mixture including the activesubstance, the conductant agent, a binder and the like on a currentcollector (for example, aluminum foil and copper foil).

As the anode active material, the carbon materials such asnon-graphitizable carbon, easily-graphitizable carbon, graphite,pyrolytic carbons, cokes, glass-like carbons, an organic polymercompound fired product, carbon fiber, or activated carbon can be listed.The materials containing at least one member selected from a group of asingle body, an alloy and a compound of metal elements capable offorming an alloy with lithium as well as a single body, an alloy and acompound of semimetal elements capable of forming an alloy with lithiumare employed (hereinafter, these are referred to as alloy-based anodeactive materials).

As the aforementioned metal element or semimetal element, tin (Sn), lead(Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony(Sb), bismuth (Bi), cadmium (Cd), magnesium (Mg), boron (B), gallium(Ga), germanium (Ge), arsenic (As), silver (Ag), zirconium (Zr), yttrium(Y) or hafnium (Hf) can be listed.

As an example of specific compounds, there exists LiAl, AlSb, CuMgSb,SiB₄, SiB₆, Mg₂Si, Mg₂Sn, Ni₂Si, TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂,CrSi₂, Cu₅Si, FeSi₂, MnSi₂, NbSi₂, TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄,Si₂N₂O, SiOv (0<v≦2), SnOw (0<w≦2), SnSiO₃, LiSiO, LiSnO or the like.

Lithium-titanium composite oxide (spinel-type composite oxide,ramstellite-type composite oxide, and the like) is also preferable.

The positive electrode active substance is acceptable so long as it is asubstance capable of absorbing and releasing lithium ion. As apreferable example, for example, composite metal oxide containinglithium and olivine-type lithium phosphate can be listed.

The composite metal oxide containing lithium is metal oxide includinglithium and transition metal. Or the composite metal oxide containinglithium is metal oxide in which one part of the transition metal in themetal oxide was replaced with different elements. The metal oxidecontaining at least one member or more selected from a group of cobalt,nickel, manganese and iron as the transition metal element is morepreferable.

As an specific example of the composite metal oxide containing lithium,for example, Li_(k)CoO₂, Li_(k)NiO₂, Li_(k)MnO₂, Li_(k)Co_(m)Ni_(1-m)O₂,Li_(k)Co_(m)M_(1-m)O_(n), Li_(k)Mn₂O₄ and Li_(k)Mn_(2-m)MnO₄ (M is atleast one element selected from a group of Na, Mg, Sc, Y, Mn, Fe, Co,Ni, Cu, Zn, Al, Cr, Pb, Sb and B. k=0 to 1.2, m=0 to 0.9, and n=2.0 to2.3) can be listed.

The compound (lithium-iron phosphorus oxide) with an olivine-typecrystalline structure represented by a general formulaLi_(x)Fe_(1-y)M_(y)PO₄(M is at least one element selected from a groupof Co, Ni, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca and Sr. 0.9<x<1.2and 0≦y<0.3) can be listed. As such lithium-iron phosphorus oxide, forexample, LiFePO₄ is preferred.

The compounds represented by a general formulaX—S—R—S—(S—R—S)_(n)—S—R—S—X′ described in European Patent No. 415856 areemployed as lithium thiolate.

The separator is configured of porous membranes made of synthetic resin(for example, polyurethane, polytetrafluoroethylene, polypropylene andpolyethylene), or porous membranes made of ceramics. The separatorhaving two kinds of the porous membranes or more laminated therein maybe used.

The electrolyte solution contains the non-aqueous solvents and theelectrolyte salts. The non-aqueous solvents are, for example, cycliccarbonate (propylene carbonate, ethylene carbonate and the like), chainesters (diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate andthe like), ethers (γ-butyrolactone, sulfolane, 2-methyltetrahydrofuran,dimethoxyethane and the like). They could be single and a mixture ofplural kinds. Carbonate is preferable from a viewpoint of oxidativestability.

The electrolyte salts are, for example, LiBF₄, LiClO₄, LiPF₆, LiSbF₆,LiAsF₆, LiAlCl₄, LiCF₃SO₃, LiCF₃CO₂, LiSCN, lower aliphatic lithiumcarboxylate, LiBCl, LiB₁₀Cl₁₀, lithium halides (LiCl, LiBr, LiI and thelike), haloborates (bis(1,2-benzenediolate(2-)-O,O′) lithium borate,bis(2,3-naphthalenediolate(2-)-O,O′) lithium borate,bis(2,2′-biphenyldiolate(2-)-O,O′) lithium borate,bis(5-fluoro-2-olate-1-benzenesulfonic acid-O,O′) lithium borate and thelike), and imide salts (LiN(CF₃SO₂)₂, LiN(CF₃SO₂)(C₄F₉SO₂), and thelike). Lithium salts such as LiPF₆ and LiBF₄ are preferable. LiPF₆ isparticularly preferable.

The gel-like electrolyte in which the electrolyte solution has been keptin the polymer compound may be employed as the electrolyte solution. Theaforementioned polymer compounds are, for example, polyacrylonitrile,poly(vinylidene fluoride), a copolymer of poly(vinylidene fluoride) andpolyhexafluoropropylene, polytetrafluoroethylene,polyhexafluoropropylene, polyethylene oxide, polypropylene oxide,polyphosphazene, polysiloxane, poly(vinyl acetate), poly(vinyl alcohol),poly(methyl methacrylate), polyacrylate, polymethacrylate,styrene-butadiene rubber, nitrile-butadiene rubber, polystyrene andpolycarbonate. The polymer compounds having structures ofpolyacrylonitrile, poly(vinylidene fluoride), polyhexafluoropropyleneand polyethylene oxide are preferable from a viewpoint ofelectrochemical stability.

The conductant agents are, for example, graphite (natural graphite,artificial graphite and the like), carbon black (acetylene black, ketjenblack, channel black, furnace black, lamp black, thermal black and thelike), conductive fiber (carbon fiber and metal fiber), metal (Al etc.)powder, conductive whiskers (zinc oxide, potassium titanate and thelike), conductive metal oxide (titanium oxide and the like), organicconductive materials (phenylene derivatives and the like) andfluorinated carbon.

The binders are, for example, poly(vinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, aramid resin,polyamide, polyimide, poly(amide-imide), polyacrylonitrile,polyacrylate, methyl polyacrylate, ethyl polyacrylate, hexylpolyacrylate, polymethacrylate, methyl polymethacrylate, ethylpolymethacrylate, hexyl polymethacrylate, poly(vinyl acetate),polyvinylpyrrolidone, polyether, polyether sulphone,hexafluoropolypropylene, styrene-butadiene rubber, modified acrylicrubber and carboxymethyl cellulose.

The negative electrode of the lithium-ion battery, as a rule, isproduced by laminating the anode active material (for example, thegraphite material) 7 on a current collecting electrode plate (forexample, copper foil) 8 (see FIG. 3). The material of the presentinvention can be employed for both of the anode active material and thecurrent collecting electrode. The material of the present invention canbe employed only for the anode active material. When the material inaccordance with the present invention is employed for the activesubstance, the nonwoven fabric can be employed as it stands. Or, thematerial in accordance with the present invention can be also employedby crushing into powder. When the material in accordance with thepresent invention is crushed into powder and is employed, the materialin accordance with the present invention can be configured only of theaforementioned carbon fiber. Additionally, the material in accordancewith the present invention may be employed together with theconventional active substances. In such a case, an amount of theaforementioned carbon fiber is preferably 0.1 to 50% by mass per anamount of all anode active materials. The case that an amount of thecarbon fiber is 1 to 30% by mass is more preferable. The case that anamount of the carbon fiber is 1 to 10% by mass is particularlypreferable.

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is also employed as the conductive auxiliary. Thematerials having no conductivity such as lithium cobalt oxide areemployed for the positive electrodes of the lithium-ion batteries. Whenthe aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is employed, the internal resistance is reduced. When thealloy-based negative electrode materials having low conductivity areemployed in lithium-ion batteries, the aforementioned carbon fibernonwoven fabric (or the aforementioned carbon fiber) can be utilized asthe conductive auxiliary of the negative electrodes. An amount of theconductive auxiliaries is 0.1 to 20% by mass (more preferably, 0.5 to10% by mass and particularly preferably, 0.5 to 3% by mass) per anamount of all active substances that are employed for the electrodes.

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is employed as a mother material of the alloy-based anodeactive material in the lithium-ion battery. When an alloy of silicon ortin and the carbon material is employed as the anode active material, acharge/discharge capacity is large. As it is, in this case, the problemthat a change in the volume of the active substance due to thecharge/discharge is large surfaces. By the way, in this case, thereexist pores in the aforementioned carbon fiber nonwoven fabric (or theaforementioned carbon fiber). Thus, when the aforementioned alloy (theanode active material) is laminated on the aforementioned carbon fibernonwoven fabric (or the aforementioned carbon fiber), that is, when theaforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is employed as the mother material of the anode activematerial, a change in the volume of the active substance at the time ofthe charge/discharge is alleviated. This allows the lithium-ion batteryhaving a high cyclic property to be obtained. With regard to theaforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) and the alloy-based anode active material, the followingratio thereof is preferable. An amount of the alloy-based anode activematerial is 0.01 to 1000% by mass per the aforementioned carbon fibernonwoven fabric (or the aforementioned carbon fiber). In addition, it is0.1 to 100% by mass. Particularly, it is 0.1 to 30% by mass.

A method of immersing the aforementioned carbon fiber nonwoven fabric(or the aforementioned carbon fiber) into a solution containing theanode active material is employed in order to affix the alloy-basedanode active material to the aforementioned carbon fiber nonwoven fabric(or the aforementioned carbon fiber). Or, a method of coating theaforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) with the solution containing the anode active material isemployed. Or, a physical depositing method or a chemical depositingmethod may be employed. For example, a vacuum evaporation method, asputtering method, an ion plating method, or a laser ablation method maybe employed. A CVD (Chemical Vapor Deposition) method may be employed. Ahot CVD method and a plasma CVD method may be employed. A wet-typeplating method may be employed instead of the above-mentioned dry-typeplating method. For example, an electroplating method or an electrolessplating method may be employed. In addition to them, a sintering methodmay be employed. For example, an atmospheric sintering method, areactive sintering method or a hot press sintering method may beemployed.

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is applied for the electrode of the capacitor. Theaforementioned capacitor is an electric double-layer capacitor. Theaforementioned capacitor is a lithium-ion capacitor. The aforementionedelectrode is preferably a negative electrode. The negative electrode ofthe lithium-ion capacitor, as a rule, is produced by laminating theanode active material (for example, a graphite material) 9 on a currentcollecting electrode plate (for example, copper foil) 10 (see FIG. 4).The material in accordance with the present invention is employed forboth of the anode active material and the current collecting electrode.The material in accordance with the present invention is employed onlyfor the anode active material. When the material in accordance with thepresent invention is employed only for the active substance, thenonwoven fabric can be employed as it stands. Or, the material inaccordance with the present invention may be employed by crushing intopowder.

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is applied for the material of the porous carbon electrodeof the fuel cell. The aforementioned fuel cell is a solid polymer typefuel cell. The aforementioned electrode is preferably an anode. Theanode of the solid polymer type fuel cell, as a rule, is produced bylaminating a catalyst layer 12 that is comprised of platinum-supportedcarbon and polymer electrolyte on a porous carbon electrode material 11(FIG. 23)

[Filter]

The aforementioned carbon fiber nonwoven fabric (or the aforementionedcarbon fiber) is employed for collecting or classifying the particles.That is, the aforementioned carbon fiber nonwoven fabric (or theaforementioned carbon fiber) is employed as a filter.

Hereinafter, the examples are listed for explaining the presentinvention. However, the present invention is not limited to thefollowing examples.

EXAMPLES Example 1

Polyvinyl alcohol of 100 g (product name: POVAL 117: produced by KURARAYCO. LTD.), mesophase pitch of 120 g (product name: AR: produced byMITSUBISHIGAS CHEMICAL COMPANY. INC.) and water of 800 g were mixed withthe beads mill. This allowed the mesophase pitch dispersion liquidhaving polyvinyl alcohol dissolved therein to be prepared. The particlediameter of the carbon particles within this dispersion liquid was 200nm (measuring apparatus: LA-950: manufactured by HORIBA, Ltd.). Theviscosity of the dispersion liquid was 4500 mPa·S (measuring apparatus:BH type Viscometer: manufactured by TOKIMEC INC.).

The electrospinning apparatus (see FIG. 1, nozzle diameter; 1.0 mm,collector (current collecting electrode); aluminum foil, distancebetween the nozzle and the collector; 10 cm, voltage: 10 kV) wasemployed. That is, the electrospinning was performed by employing theabove-mentioned dispersion liquid. The nonwoven fabric made of thecarbon fiber precursors was produced on the collector.

The above-mentioned nonwoven fabric was laminated. This laminatednonwoven fabric was heated for 10 minutes at a temperature of 150° C. inthe air. Thereafter, it was heated for one hour at a temperature of 300°C.

Thereafter, the laminated nonwoven fabric was heated at a temperature ofup to 900° C. under an argon gas atmosphere.

Next, the laminated nonwoven fabric was heated at a temperature of up to2800° C. in a graphitizing furnace.

In a manner mentioned above, the graphitized carbon fiber nonwovenfabric in accordance with the present invention was obtained.

The SEM photograph of the graphitized carbon fiber nonwoven fabricobtained in this example (SEM apparatus: name of apparatus: VE-8800manufactured by KEYENCE CORPORATION) is shown in FIG. 5. According tothe above SEM photograph, the fiber constituting the nonwoven fabric wasfiber having irregularities. That is, the aforementioned fiber includeda large diameter portion (the diameter: approximately 500 to 1000 nm)and a small diameter portion (the diameter: approximately 100 to 200nm). The length of the aforementioned large diameter portion wasapproximately 500 to 1000 nm. The length of the aforementioned smalldiameter portion (the distance between the aforementioned large diameterportion and the aforementioned large diameter portion) was approximately500 to 1000 nm.

The thickness of the aforementioned nonwoven fabric was 125 μm and theweight thereof was 210 g/m². The BET surface area (measurementapparatus: manufactured by Shimadzu Corporation) was 10.8 m²/g.

The XRD measurement result of the graphitized carbon fiber nonwovenfabric obtained in this example (XRD apparatus: manufactured by RigakuCorporation) is shown in FIG. 6. The half width in this maximum peak was0.95°.

The Raman measurement result of the graphitized carbon fiber nonwovenfabric obtained in this example (Raman measurement apparatus:manufactured by Shimadzu Corporation) is shown in FIG. 7. According tothis, ID/IG was 0.87.

The S/L measurement was performed by employing the above-mentioned SEMphotograph. That is, imageJ (US National Institute of MentalHealth/National Institute of Neurological Disorders and Stroke, ResearchSupport Branch HP http://rsb.info.nih.gov/ij/index.html) was employed.The carbon fiber portion and the portion other than the carbon fiberwere separated, and the area and the length of the circumference of thecarbon fiber portion were measured. The image subjected to theprocessing is shown in FIG. 8. As a result, L/(S)^(1/2)=140 was yielded.As a result of measuring the similar image, (the maximum value in thelarge diameter portion)/(the minimum value in the small diameterportion)=10 was yielded.

Example 2

The processing similar to that of the example 1 was performed exceptthat an amount of the mesophase pitch was 100 g. A result thereof isshown in Table 1. The SEM photograph of the graphitized carbon fibernonwoven fabric of this example (SEM apparatus: VE-8800 manufactured byKEYENCE CORPORATION) is shown in FIG. 9. Further, the image employed foran image analysis of the SEM photograph is shown in FIG. 10.

Example 3

Polyethylene oxide of 100 g (product name: Polyethylene Glycol2,000,000: produced by Wako Pure Chemistry Industries, Ltd.), mesophasepitch of 200 g (product name: AR) and water of 700 g were mixed with thebeads mill. This allowed the mesophase pitch dispersion liquid havingpolyethylene oxide dissolved therein to be prepared. The particlediameter of the carbon particles within this dispersion liquid was 150nm (measuring apparatus: LA-950). The viscosity of the dispersion liquidwas 100 mPa·S (measuring apparatus: BH type Viscometer).

The electrospinning was performed similarly to that of the example 1 byemploying this dispersion liquid. That is, the nonwoven fabric made ofthe carbon fiber precursors was produced on the collector.

The above-mentioned nonwoven fabric was laminated. This laminatednonwoven fabric was heated for one hour at a temperature of 100° C. inthe air. Thereafter, it was heated for one hour at a temperature of 200°C.

Thereafter, the laminated nonwoven fabric was heated at a temperature ofup to 900° C. under the argon gas atmosphere.

Next, the laminated nonwoven fabric was heated at a temperature of up to2400° C. in the graphitizing furnace.

In a manner mentioned above, the graphitized carbon fiber nonwovenfabric in accordance with the present invention was obtained.

Properties of the nonwoven fabric of this example are shown in Table 1.

Example 4

Polyacrylic acid of 20 g (product name: AQUALIC AS58: produced by NIPPONSHOKUBAI CO., LTD), mesophase pitch of 30 g (product name: AR) and waterof 950 g were mixed with the beads mill. This allowed the mesophasepitch dispersion liquid having polyacrylic acid dissolved therein to beprepared. The particle diameter of the carbon particles within thisdispersion liquid was 400 nm (measuring apparatus: LA-950). Theviscosity of the dispersion liquid was 120 mPa·S (measuring apparatus:BH type Viscometer).

The electrospinning was performed similarly to that of the example 1 byemploying this dispersion liquid. That is, the nonwoven fabric made ofthe carbon fiber precursors was produced on the collector.

The above-mentioned nonwoven fabric was laminated. This laminatednonwoven fabric was heated for one hour at a temperature of 150° C. inthe air. Thereafter, it was heated for one hour at a temperature of 300°C.

Thereafter, the laminated nonwoven fabric was heated at a temperature ofup to 900° C. under the argon gas atmosphere.

Next, the laminated nonwoven fabric was heated at a temperature of up to2800° C. in the graphitizing furnace.

In a manner mentioned above, the graphitized carbon fiber nonwovenfabric in accordance with the present invention was obtained.

Properties of the nonwoven fabric of this example are shown in Table 1.

Example 5

Polyvinylbutyral of 100 g (product name: Mowital: produced by KURARAYCO. LTD.), mesophase pitch of 100 g (product name: AR) and isopropylalcohol of 800 g were mixed with the beads mill. This allowed themesophase pitch dispersion liquid having polyvinylbutyral dissolvedtherein to be prepared. The particle diameter of the carbon particleswithin this dispersion liquid was 350 nm (measuring apparatus: LA-950).The viscosity of the dispersion liquid was 320 mPa·S (measuringapparatus: BH type Viscometer).

The electrospinning was performed similarly to that of the example 1 byemploying this dispersion liquid. That is, the nonwoven fabric made ofthe carbon fiber precursors was produced on the collector.

The obtained nonwoven fabric was heated for two hours at a temperatureof 150° C. in the air. Thereafter, it was heated for one hour at atemperature of 300° C.

Thereafter, the nonwoven fabric was heated at a temperature of up to900° C. under the argon gas atmosphere.

Next, the nonwoven fabric was heated at a temperature of up to 2800° C.in the graphitizing furnace.

In a manner mentioned above, the graphitized carbon fiber nonwovenfabric in accordance with the present invention was obtained.

Properties of the nonwoven fabric of this example are shown in Table 1.

Example 6

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 190 g. A result thereof isshown in Table 1.

Example 7

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 150 g. A result thereof isshown in Table 1.

Example 8

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 70 g. A result thereof isshown in Table 1.

Example 9

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 50 g. A result thereof isshown in Table 1.

Example 10

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 30 g. A result thereof isshown in Table 2.

Example 11

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 220 g. The result thereof isshown in Table 2.

Example 12

The processing was performed similarly to that of the example 1 exceptthat an amount of the mesophase pitch was 10 g. The result thereof isshown in Table 2.

Example 13

The processing was performed similarly to that of the example 1 exceptthat an amount of polyvinyl alcohol is 60 g, an amount of the mesophasepitch was 70 g, and water is 870 g. The result thereof is shown in Table2.

The SEM photograph of the graphitized carbon fiber nonwoven fabric ofthis example (SEM apparatus: VE-8800 manufactured by KEYENCECORPORATION) is shown in FIG. 11.

Example 14

Carboxymethylcellulose amine salt of 50 g (product name: Ammonium CMCDN-400H: produced by DAICEL CHEMICAL INDUSTRIES, LTD.), mesophase pitchof 50 g (product name: AR) and water of 900 g were mixed with the beadsmill. This allowed the mesophase pitch dispersion liquid havingcarboxymethylcellulose amine salt dissolved therein to be prepared. Theparticle diameter of the carbon particles within this dispersion liquidwas 230 nm (measuring apparatus: LA-950). The viscosity of thedispersion liquid was 8300 mPa·S (measuring apparatus: BH typeViscometer).

The electro spinning was performed similarly to that of the example 1 byemploying this dispersion liquid. That is, the nonwoven fabric made ofthe carbon fiber precursors was produced on the collector.

The obtained nonwoven fabric was heated for one hour at a temperature of300° C. in the air.

Thereafter, the nonwoven fabric was heated at a temperature of up to900° C. under the argon gas atmosphere.

Next, the nonwoven fabric was heated at a temperature of up to 2800° C.in the graphitizing furnace.

In a manner mentioned above, the graphitized carbon fiber nonwovenfabric in accordance with the present invention was obtained.

Properties of the nonwoven fabric of this example are shown in Table 2.

Example 15

Polyvinyl alcohol of 100 g (product name: POVAL 117), mesophase pitch of20 g (product name: AR) and water of 800 g were mixed with the beadsmill. This allowed the mesophase pitch dispersion liquid havingpolyvinyl alcohol dissolved therein to be prepared. The particlediameter of the carbon particles within this dispersion liquid(measuring apparatus: LA-950) was 200 nm. The viscosity of thedispersion liquid was 4300 mPa·S (measuring apparatus: BH typeViscometer).

The electrospinning was performed similarly to that of the example 1 byemploying this dispersion liquid. That is, the nonwoven fabric made ofthe carbon fiber precursors was produced on the collector.

The above-mentioned nonwoven fabric was laminated. This laminatednonwoven fabric was heated for ten minutes at a temperature of 150° C.in the air. Thereafter, it was heated for one hour at a temperature of300° C.

Thereafter, the laminated nonwoven fabric was heated at a temperature ofup to 900° C. under the argon gas atmosphere.

Next, the laminated nonwoven fabric was heated at a temperature of up to2400° C. in the graphitizing furnace.

In a manner mentioned above, the graphitized carbon fiber nonwovenfabric in accordance with the present invention was obtained.

Properties of the nonwoven fabric of this example are shown in Table 2.

Comparative example 1

The production of the nonwoven fabric was tried with melt flow method byemploying the dispersion liquid of the example 1. However, the nonwovenfabric was not obtained.

Comparative example 2

The processing was performed similarly to that of the example 1 exceptthat, instead of the dispersion liquid of the example 1 (the mesophacepitch dispersion liquid having polyvinyl alcohol dissolved therein), apolyvinyl alcohol aqueous solution (polyvinyl alcohol (product name:POVAL 117)) of 100 g, and water 900 g were employed, and that the carbonblack and the pitch were not included.

The diameter of the fiber of the nonwoven fabric obtained in thiscomparative example 2 was uniform (50 nm). That is, there was no fiberincluding both of the large diameter portion and the small diameterportion on a piece by piece basis.

Example 16

The carbon fiber nonwoven fabric obtained in the example 1 waspulverized by employing a mortar. The pulverizing allowed the carbonfiber to be obtained.

An investigation similar to that of the example 1 was carried out forthe above carbon fiber. A result thereof is shown in Table 2. The SEMphotograph of the graphitized carbon fiber nonwoven fabric of thisexample (SEM apparatus: VE-8800 manufactured by KEYENCE CORPORATION) isshown in FIG. 12. Further, the image subjected to the processingemployed for an image analysis of the SEM photograph is shown in FIG.13.

Example 17

The processing was performed similarly to that of the example 16 exceptthat the carbon fiber nonwoven fabric obtained in the example 13 wasemployed.

An investigation similar to that of the example 1 was carried out forthe above carbon fiber. A result thereof is shown in Table 2. The SEMphotograph of the graphitized carbon fiber nonwoven fabric of thisexample (SEM apparatus: VE-8800 manufactured by KEYENCE CORPORATION) isshown in FIG. 14.

Comparative example 3

This is an example described in Non-Patent literature 1. Thermoplasticresin (poly(4-methyl pentene-1): TPX: Grade RT-18 produced by MitsuiChemicals, Inc.) of 70 g, mesophase pitch of 30 g (product name: AR)were mixed with the ball mill (P-7: manufactured by Fritsch GmbH.). Thismixture was kneaded by a kneader (apparatus name: Laboratory MixingExtruder Model CS-194AV: manufactured by ATLAS ELECTRIC DEVICES,COMPANY) at a temperature of 240° C. The spinning was performed with themelt blow method by employing the above kneaded product. The kneadingconditions are as follows. The nozzle is a single-hole nozzle with adiameter of 0.5 mm (manufactured by NIPPON NOZZLE CO., LTD). Thespinning temperature is 380° C. The resin pressure is 0.4 MPa. The blowpressure is 3.5 MPa. The obtained fiber was thermally treated for 24hours at a temperature of 160° C. under the oxygen atmosphere.Thereafter, the obtained fiber was thermally treated for one hour at atemperature of 900° C. and thermally treated for thirty minutes at atemperature of 3000° C. under the nitrogen atmosphere.

The SEM photograph of the fiber obtained in such a manner is shown inFIG. 15. The fiber diameter was 100 nm to 5 μm. The dispersion of thefiber diameters between each fiber and the other was recognized to belarge. However, the fiber diameter was uniform on a piece by piecebasis. That is, there was no fiber including both of the large diameterportion and the small diameter portion.

Comparative example 4

This an example described in Non-Patent literature 2. Polyacrylonitrile(molecular weight 86220: produced by Aldrich Corporation) of 5 g wasdissolved in DMF of 45 ml. And, the electrospinning (voltage: 25 kV, thecollecting plate: aluminum foil and nozzle: 0.5 mm) was performed. Theobtained nonwoven fabric was thermally treated for one hour at atemperature of 280° C. in the air. Thereafter, it was thermally treatedat a temperature of 2800° C. in the argon.

The SEM photograph of the obtained fiber is shown in FIG. 16. The fiberdiameter was uniform (100 nm). That is, there was no fiber includingboth of the large diameter portion and the small diameter portion on apiece by piece basis.

Example 18

The electrodes were produced. The anode active material of the aboveelectrodes is the fiber of the example 15. Lithium was employed for thecounter electrodes, and a charge/discharge measurement was made. Thisresult is shown in FIG. 17. A charge/discharge capacity was 200 mAh/g.

Thus, the carbon fiber of the example 13 is preferred as the negativeelectrode material for the lithium-ion secondary battery.

Example 19

The electrodes were produced. The anode active material of the aboveelectrodes is the nonwoven fabric of the example 1. Lithium was employedfor the counter electrodes, and a charge/discharge measurement was made.This result is shown in FIG. 18.

Thus, the nonwoven fabric of the example 1 is preferred as the negativeelectrode material for the lithium-ion secondary battery.

Example 20

The electrodes were produced. The anode active material of the aboveelectrodes is the nonwoven fabric of the example 6. Lithium was employedfor the counter electrodes, and a charge/discharge measurement was made.As a result, a charge/discharge capacity was 210 mAh/g.

Thus, the nonwoven fabric of the example 6 is preferred as the negativeelectrode material for the lithium-ion secondary battery.

Example 21

The electrodes were produced. The anode active material of the aboveelectrodes is the nonwoven fabric of the example 10. Lithium wasemployed for the counter electrodes, and a charge/discharge measurementwas made. As a result, the charge/discharge capacity was 150 mAh/g.

Thus, the c nonwoven fabric of the example 10 is preferred as thenegative electrode material for the lithium-ion secondary battery.

Example 22

The electrodes were produced. The anode active material of the aboveelectrodes is the nonwoven fabric of the example 11. Lithium wasemployed for the counter electrodes, and the charge/dischargemeasurement was made. As a result, the charge/discharge capacity was 220mAh/g.

Thus, the nonwoven fabric of the example 11 can be employed for thenegative electrode materials for the lithium-ion secondary battery.However, the nonwoven fabric of the example 11 is difficult to handle ascompared with that of the example 1.

Example 23

The electrodes were produced. The anode active material of the aboveelectrodes is the nonwoven fabric of the example 12.

Lithium was employed for the counter electrodes, and thecharge/discharge measurement was made. As a result, the charge/dischargecapacity was 100 mAh/g.

Thus, the nonwoven fabric of the example 12 can be employed for thenegative electrode materials for the lithium-ion secondary battery.However, the charge/discharge capacity declined as compared with that ofthe example 1.

Comparative example 5

The electrodes were produced. The anode active material of the aboveelectrodes is the nonwoven fabric of the comparative example 2. Lithiumwas employed for the counter electrodes, and the charge/dischargemeasurement was made. As a result, the charge/discharge capacity was 0mAh/g, and the above electrodes did not function as the negativeelectrode material at all.

Comparative example 6

Lithium cobalt oxide (produced by Hohsen Corp.) of 96 g, polyvinylidenedifluoride (produced by Sigma-Aldrich Corporation) of 2 g and acetyleneblack (produced by DENKI KAGAKU KOGYO KABUSHIKI KAISYA) of 2 g weremixed. Addition of N-methylpyrrolidone hereto yielded the paste-likemixture. The copper foil was coated with the above paste-like mixture bya bar-coater so that a membrane thickness after the drying was 20 μm.Thereafter, the drying was performed, and the positive electrodes forthe lithium-ion secondary batteries were produced. The SEM photograph isshown in FIG. 19.

The surface electric resistance of the above positive electrodes wasmeasured with a four-point probe method (manufactured by MitsubishiChemical Analytech Co., Ltd.). A result thereof was 0.4Ω/□.

Example 24

The processing was performed similarly to that of the comparativeexample 6 except that the carbon fiber of 2 g obtained in the example 17was employed instead of acetylene black. And, the positive electrodesfor the lithium-ion secondary batteries were produced. The SEMphotograph is shown in FIG. 20.

The surface electrical resistance of the above positive electrodes wasmeasured with the four-point probe method (manufactured by Mitsubishichemical Analytech Co., Ltd.). A result thereof was 0.2Ω/□.

Comparative example 7

The Si membrane (the membrane thickness: 500 nm) was mounted on thecopper foil with the vapor deposition (vapor deposition apparatus:UEP-4000 manufactured by ULVAC, Inc.). And the negative electrodes wereproduced. Lithium was employed for the counter electrodes.

The charge/discharge measurement was made. A result thereof was shown inFIG. 21. The charge/discharge capacity of the first cycle was 580 mAh/g.The capacity declined during repetition of the charge/discharge cycle.

Example 25

The processing was performed similarly to that of the comparativeexample 7 except that the carbon fiber nonwoven fabric obtained in theexample 13 was employed instead of the copper foil. An amount of Si was17% by mass per the carbon fiber nonwoven fabric. Lithium was employedfor the counter electrodes.

The charge/discharge measurement was made. A result thereof was shown inFIG. 22. The charge/discharge capacity was 667 mAh/g. The capacity didnot decline even though the charge/discharge cycle was repeated. It canbe grasped that the cyclic property was enhanced as compared with thecomparative example 7 employing the copper foil for the mother material.

Example 26

The nonwoven fabric of the example 8 was coated with a mixed paste ofplatinum-supported carbon and polymer electrolyte (produced by ChemixInc.). After the coating, the above nonwoven fabric was dried for tenminutes at a temperature of 100° C. And, the anode electrode for thesolid polymer type fuel cell was produced. The cross-sectional schematicview of the above anode electrode is shown in FIG. 23, and the SEMphotograph of the obtained sample is shown in FIG. 24.

The obtained anode electrode, and the cathode electrode, the solidpolymer electrolyte membrane and the carbon separator each of which wasproduced by Chemix Inc. were employed, and the solid polymer type fuelcells were produced.

As a result of introducing hydrogen from the anode and measuring anopen-circuit voltage, the open-circuit voltage was 0.98 V.

Example 27

Lithium was inserted into the nonwoven fabric of the example 8 by a halfof the maximum capacity with a method similar to that of the example 17,and the negative electrodes were produced. The positive electrodes wereproduced by use of the active carbon. The electrolyte solution wasprepared by employing ethylene carbonate containing lithiumhexafluorophosphate and diethyl carbonate.

After the charge up to 4 v was carried out, the discharge was carriedout up to 3 v at a constant output. A correlation between an energydensity and an output density was measured. A result thereof is shown inFIG. 25.

It can be grasped that the capacity is large in a high-rate area ascompared with that of the comparative example 7.

Comparative example 8

This an example described in Non-Patent literature 3. A measurementsimilar to that of the example 27 was made except that the graphiteparticles having a diameter of 10 μm were employed for the negativeelectrode. A result thereof is shown in FIG. 25.

Example 28

A mixed solution of a dispersion liquid of the carbon particles having adiameter of 400 nm, and a dispersion liquid of silicon oxide having adiameter of 10 nm was prepared. The above mixed solution was filteredwith the nonwoven fabric (filter) of the example 13. As a result, onlysilicon oxide having a diameter of 10 nm was filtered (passed).

[Properties]

TABLE 1 EX. 1 EX. 2 EX. 3 EX. 4 EX. 5 EX. 6 EX. 7 EX. 8 EX. 9 Resin PVAPVA PEO PAA PVB PVA PVA PVA PVA Carbon/resin (wt/wt) 120/100 100/100200/100 30/20 100/100 190/100 150/100 70/100 50/100 Small diameterportion 100 50 100 20 200 50 600 300 30 minimum value (nm) Largediameter portion 500 300 1000 30 250 1500 1000 500 100 minimum value(nm) Large diameter portion 1000 1000 1500 50 300 2000 1500 700 200maximum value (nm) Small diameter portion 1000 100 600 100 200 20 3002000 3000 length (nm) Large diameter portion 1000 2000 1000 100 500 60003000 500 300 length (nm) Nonwoven fabric 125 130 1010 0.5 10 200 185 210165 thickness (μm) Nonwoven fabric weight 210 200 820 0.9 13 195 165 155172 (g/m²) BET surface area 10.8 5.8 15.6 5.4 8.6 5.6 4.9 16 24 (m²/g)XRD (half width) 0.95 0.50 0.20 0.30 1.6 0.30 0.45 1.50 1.65 Ramanscattering 0.67 0.28 0.75 1.53 1.32 0.23 0.35 0.53 0.85 (ID/IG) SEMobservation 140 84 75 230 65 43 86 164 153 (L/(S)^(1/2)) SEM observation(*) 10 20 15 2.5 1.5 40 1.6 2.3 6.7

TABLE 2 EX. 10 EX. 11 EX. 12 EX. 13 EX. 14 EX. 15 EX. 16 EX. 17 ResinPVA PVA PVA PVA CMC PVA PVA PVA Carbon/resin (wt/wt) 30/100 220/10010/100 60/70 50/50 20/100 120/100 60/70 Small diameter portion 10 50 30100 500 20 100 100 minimum value (nm) Large diameter portion 30 1500 35150 1000 30 500 150 minimum value (nm) Large diameter portion 100 250040 500 1500 100 1000 500 maximum value (nm) Small diameter portion 800050 50 100 100 3000 1000 100 length (nm) Large diameter portion 100 250050 200 1000 300 1000 200 length (nm) Nonwoven fabric 150 100 50 30 10300 — — thickness (μm) Nonwoven fabric weight 130 68 34 10 15 280 — —(g/m²) BET surface area 35 5.4 45 10.4 8.9 26 15.6 15.2 (m²/g) XRD (halfwidth) 1.50 0.37 1.57 0.70 1.72 1.85 0.95 0.70 Raman scattering 0.750.31 1.02 0.25 1.64 1.05 0.87 0.25 (ID/IG) SEM observation 264 5 180 9775 120 110 86 (L/(S)^(1/2)) SEM observation (*) 10 50 1.3 5.0 3.0 5.0 105.0

*SEM observation (*): (maximum value in large diameter portion)/(minimumvalue in small diameter portion)

This application is based upon and claims the benefit of priority fromJapanese patent application No. 2010-11457, filed on Jan. 21, 2010, thedisclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

-   -   1 and 5 spinning dope supplying apparatus    -   2 and 6 exits    -   3 voltage applying apparatus    -   4 collector    -   7 and 9 anode active materials    -   8 and 10 current collecting electrode plates    -   11 porous carbon electrode material    -   12 catalyst layer

1-19. (canceled)
 20. A carbon fiber: wherein said carbon fiber includes a large diameter portion and a small diameter portion; wherein a diameter of said large diameter portion is 20 nm to 2 μm; wherein a diameter of said small diameter portion is 10 nm to 1 μm; and wherein (the diameter in said large diameter portion)>(the diameter in said small diameter portion).
 21. The carbon fiber as claimed in claim 20, wherein (a maximum value of the diameter in said large diameter portion)/(a minimum value of the diameter in said small diameter portion) is 1.1 to
 100. 22. The carbon fiber as claimed in claim 20, wherein a length of said small diameter portion is longer than a minimum value of the diameter in said large diameter portion.
 23. The carbon fiber as claimed claim 20, wherein the length of said small diameter portion is shorter than the maximum value of the diameter in said large diameter portion.
 24. The carbon fiber as claimed in claim 20, wherein the length of said small diameter portion is 10 nm to 10 μm.
 25. The carbon fiber as claimed in claim 20, wherein the length of said large diameter portion is 50 nm to 10 μm.
 26. The carbon fiber as claimed in claim 20, wherein said carbon fiber includes said large diameter portions in plural number, and yet said small diameter portions in plural number; and wherein a length of said carbon fiber is 0.1 to 1000 μm.
 27. The carbon fiber as claimed in claim 20, wherein a specific surface area of said carbon fiber is 1 to 100 m²/g.
 28. The carbon fiber as claimed in claim 20, wherein a peak originating in a graphite structure (002) exists within a range of 25° to 30° (2θ) in an X-ray diffraction measurement of said carbon fiber, and a half width of said peak is 0.1° to 2° (2θ).
 29. The carbon fiber as claimed in claim 20, wherein ID/IG of said carbon fiber is 0.2 to 2 (ID is a peak intensity existing within 1300 cm⁻¹ to 1400 cm⁻¹ in Raman scattering spectra of said carbon fiber. IG is a peak intensity existing within 1580 cm⁻¹ to 1620 cm⁻¹ in Raman scattering spectra of said carbon fiber.).
 30. The carbon fiber as claimed in claim 20, wherein L/(S)^(1/2) of said carbon fiber (S is an area of said carbon fiber in an image obtained by observing said carbon fiber with a scanning electron microscope. L is an outer length of said carbon fiber in the image obtained by observing said carbon fiber with the scanning electron microscope.) is 3.7 to
 300. 31-48. (canceled)
 49. A carbon fiber nonwoven fabric comprising 50 to 100% by mass of the carbon fiber of claim
 20. 